 Hello everyone, welcome to rural water resource management course, which is the NPTEL course focusing on rural water issues and how to manage them. This is week seven and we are at lecture three. In this week, we have been looking at the water balance equation, how to construct one, what are the data that gets into the equation. Today, we'd be looking at more specifics on how to solve issues and concerns using the water balance equation. Also, some important concepts will be discussed. The first one is of course the units for water balance. Because most of the time, the complex equation will have different water resources, for example groundwater, rainfall, infiltration, etc. These units might be procured or assumed or estimated from a different entity. For example, ET, we take the crop growth and then using the crop growth, crop coefficient, we understand how much water is needed. And these might trigger a difference in units. So you need to be very careful to normalize across the equation with a single unit. Let's take our example for today. The water balance equation that we have been seeing, which is del S storage or change in storage, the P which is your presentation, we are only looking at the import to keep it simple. Qs are the runoff, discharge coming in and discharge going out. Your ET, which is the plant consumption, groundwater in and groundwater out, which is given by G. The units need to be consistent. Otherwise, we'll be comparing apples and oranges, which means if the units are different, your del S might be too small, miniscule or too big, which cannot happen. You've seen a lot of works that have not normalized and by that time, the data has been published. So be very careful to have the exact units across, not only the quantity of the unit, but also the time, which means what is the unit of time that has been discussed? When I say del S, del S across what? Is it a day? Is it an hour? Or is it a month or annual? So you can pick any day, any time that goes into your equation, but keep that time consistent just between seconds and a year, just between seconds and an hour. You see the unit can change, your magnitude can change multiple times if you use the wrong unit. Usually a rate per unit time, but it's not explicitly given here. For example, when you write it, most people would write del S as millimeters, presentation as millimeters, Qn millimeters, Qr millimeters, ET, G, G out millimeters. Because when we define the water balance equation somewhere, the author would have defined it as water balance annual or daily water balance. So sometimes your unit of time is implicit. It's not as explicit as your parameters. P is rainfall millimeters or inches. So be careful to understand the unit when you have seen the water balance equation. So always good to go back and check, are they doing it correctly? Is it is correctly what you want? If time is common across, it may not be explicitly included. As I mentioned, if time is the only unit across, they won't put millimeters per year because annually they have defined. Let's take an example for water balance. Here, where is the time? It is implicit, which means you have the time here as months. So you have a total of 12 months for a particular year. So you have a particular year and you've taken 12 months. And monthly, these are the parameters values. And for our equation, we have EPT, which is your evapotranspiration together with potential. And then UP, which is your rainfall, which is your ET, which is your actual evapotranspiration. And then SMU, we had it as soil moisture deficit with SMD. And soil moisture utilization with SMU, actual soil moisture, storage, et cetera, et cetera. We're not getting to the units of these or what they actually mean because this is for showing the example of how the units are the same across. The ET, which is a measure of water getting into the plan and transpiring. Consumption, which converts into a gaseous phase and goes up, is in millimeters. So think about this. The phase would also change. The presentation, which is your rainfall, is in millimeters. You have a tube, you can measure it. But your ET, which is in a gaseous phase, is also measured as a thickness, millimeters, not as a volume. Similarly, your ice, for example, if it's a solid, you say soil water coming from your snow melt, which is actually initially was a snow thickness. So you have a millimeter of snow thickness, which converts to runoff, which converts to soil moisture. So to keep that flow uniform, the unit has been kept in uniform across the table. And as I said, you will not have a unit explicitly mentioned if it is a common unit. Here it is month. A quick question is, what was this unit for time? If you think about it, the months have been total, which means added. So all the months have been summed up. So this is the sum of all the ET and some of all your rainfall. Your actual ET, et cetera, et cetera. What you see here is the total is an annual time step, which means the unit time is annual per year. It is not per month as you see here. So let it keep it across. And then we will see how things rearrange, et cetera. Just for the quick analysis, let's do a quick seeing what this actually means, this water balance. So you have total 1,375 millimeters per year, which is the total water a plant needs in a hygienic or good condition, which means an unlimited water supply for a good growth. But the actual precipitation is only 1,134. And out of the 1,134, which is lesser than your plant requirement, not all water has been taken up because some runoff, some go to evaporation on the site, et cetera, et cetera. So you have only 952. So 952 minus P gives you your actual SMU, which is soil moisture utilization, how much unused or kept in it and the deficit. So coming back, deficit is just these two numbers because you have the potential ET, which is the highest, but the actual ET is much lesser. So you could now use a water balance approach to identify what is the soil moisture use? What is the soil moisture deficit? How much should I augment? Or how much water should my groundwater be supplied? This exercise could have been only possible by first normalizing your parameters on a specific unit and also normalizing it on a time unit. You cannot have monthly for EPT, and for this example, January, and then keep it annual for precipitation. It cannot be done. If you have only annual, what do you do? Like the least common denominator approach, you just come back here and say, OK, what is the smallest time that is across the series, which is same? But here if you say precipitation is in annual, then you have to sum everything and only look at this column and row. Only the total column and row should be taken up. Because precipitation is in annual, but here we have the division. So we kept it. If you don't have it, in some cases, you may not have it. So be careful on just using the annual so you can sum it up. But don't divide your rainfall by 12 and put it here. It is not correct because for January, you cannot put an average rainfall which is divided from it or to rainfall. So keep your rainfall. Look at it. It starts very low and then goes up and comes down. All these are tied with the planned growth and the circulation of climate. So here keep it at annual scale if that is the least common time frame that agrees across your parameters. Moving on, meet the source data from multiple organizations. This is another issue or concern. Based on the equations complexity, you may have to get data from different organizations. This happens across the world. It's not only in India or rural sectors. Wherever you go, you will have different agencies monitoring different data. To bring them together, we need to work on some mechanisms or the user has to maintain a table of data and source and pick each source of data and reorganize the units, both the time and the actual quantities parameters unit. Let's take an example for Indian case. The surface water, which is your discharge runoff, is monitored by the Central Water Commission. This is CWC. However, the groundwater is monitored by the CGWC, Central Ground Water Board. In some cases, we have the government data. So IMD is monitoring your rainfall data, which is also government. All these are government agencies. And then there's a government agency which monitors remote sensing data. And the remote sensing can be of groundwater, of surface water, rainfall, ET, you can name it. I'm only naming the parameters for your water balance equation. So it is very important to understand these units and understand the source. There could be some errors in the source, which you need to incorporate, especially for remote sensing data. They will give you some parameters that you need to incorporate to get the final output. So that is also important to read about the data before you incorporate into your water balance equation. Read the source, the methodology, how the data is collected, the units for the actual quantity, as in millimeters or inches or foot, and the time frame, which was collected, the timestamp, temporal resolution we call. Is it per day, per hour, per month, et cetera. For example, rainfall can be collected per day. So what you should do is in the IMD portal, when you download the data, you should say, no, I want it as a monthly, so that it automatically sums it and gives it to you. Otherwise, you'll have to do it by downloading the data and then making sure you use your tables to sum it up to the least common time frame. Remote sensing data can be one single entity, but multiple data. So what you saw in surface water, groundwater, and also the state water department, which is the PWDs we call in India, have data in focused parameters. For example, CWC is surface water, CGWD is groundwater, but remote sensing units like NASA for the global and US regions, and ISRO for mostly Indian regions, you would find that the data of multiple parameters is kept as an archive in the data piece. Would it be able to replace the observation data? Not possible, but you can work it together. So my point is make your equation, try to see if you can get observation data, otherwise try to see if you can go to the field and collect data. The final step is if you cannot get the data from an organization, if you cannot go collect the data, maybe it's parsley, dine consuming, et cetera, use remote sensing data. All these are accepted norms in the government because ISRO is a government data board. And you can see here how, for example, a climatic event progresses per day. So this is at very hourly or even sub minute levels. It runs, the time runs, and then you have the rainfall pattern emerging. So where the higher rainfall and millimeters, look at the units. All of them are given in your remote sensing data. You have a legend which gives you the units, which is millimeters. The color gives red means, for example, is around 42, 60 millimeters. And the unit is given here. So normally what you do, you take it as an annual stamp, daily stamp, or three-hourly stamp and do your calculations. Here you see the flooding, which is your surface water drainage water or your discharge water. And you put that in your equation for R. You remember R we use for runoff. That is this data. If it comes too much, it is flooding. And so this data was taken for the August 2018 floods in Kerala, which was a very devastating floods, a hundred year flood in Kerala. And you can see the water level depth as meters. So look here very carefully. It is in meters. You need to convert to millimeters. If you find it very hard, I'll give you some tricks how to do the conversions, et cetera. Let's look at some central groundwater estimate type of water balance equation. You have the annual replenishable groundwater resource as 433 billion cubic meter. So in a millimeter you have, and now this is a volume. So you have a thickness and you have volume. The thickness can be converted to a volume by just multiplying across the area. They would have some different methods. Please look at the source and see how they estimate it. So the net annual groundwater availability is 398 billion cubic meters. Annual groundwater draft for irrigation domestic is 245 billion cubic meters, which is one of the biggest in the world. And it is the biggest ranked number one highest consumption of groundwater. Stage of groundwater development is 62%. So here in the three variables are enough to set up a good groundwater water balance. You have the annual 433 on one side and then you have your net groundwater availability 398 and the use is 245. So what is the storage? 398 minus 245 could be the storage and that's what gives you a 62%. And you can also understand from 433 only 398. So approximately 35 million cubic meters is not available, but it gets replenished. So that could be the water that goes into the base flow river discharge, et cetera. So these do give a clear picture. What are the units are not consistent? As I promised, I'll give you the tricks. Go back and convert to a common unit. I would stick to SI metric units so that it is more commonly used rather than the gallons and foot break, those kind of conversions. Convert to a common timing, for example, day month year, most of these parameters are done monthly and then annually. From the month, you can take the seasonal, so which is very smart. You cannot do a year and then come back to seasonal, because the season's water is important. You're Ravi, you're Karif, which is your monsoon season, the Ravi, which is your non-monsoon and then you have the winter crops. Sometimes the winter crops is clung with the Ravi. So you can have the two key ones for water irrigation as Karif and Ravi season. If you cannot convert it manually and all through your table or formula like Excel or open source library, open office, et cetera, what you could do is use online open source tools. Just type it in Google meters to foot cubic meters to foot takeer, it'll do it automatically. Do just check it out, but most of the time it is accurate. So do it and these kind of handbooks or something that could be stuck on your reading room when you're doing these calculations. These conversions do help you arithmetically to think about these numbers, how they have been sourced. But most importantly, you should not be wasting putting too much time on each and every conversion because sometimes you can do a small mistake. For example, you say to convert, just multiply from centimeters to inches, 0.394. If you just put 0.0394 in your computer Excel, for example, then the whole table is gone. So be careful with these changes, double check your work. And always compare randomly test one variable, put it in Google and say, for example, 50 millimeters into inches test what it is and then double check, always double check. And it's better to use metric units, not English units because most of the data that you get from online open source is metric, not English. I'll tell you, for example, cricket is in yards, but our road length and the time to get is in kilometers. So you see how it's confusing. We just keep it in meters. We don't call 22 meters or 10 meters for the cricket pitch, we say yards. We say in feet, foot for the height. We could have just kept it in meters and centimeters like they use it for selection committees. So like that, just keep it in one, which is very, very important for your water balance. Moving on, measurements and units for water balance. Let's take our example again. When you do this example, it is as important to also identify the area and unit of study. This has to be the first that you should be doing. Then you look at your data availability units, et cetera. Why did I bring it after is so that to give a clear picture of your units, availabilities, et cetera, and pan your area you could check. For example, I'm gonna do it in Chennai and I would like to see what data sources are available in Tamil Nadu and the government so that I could check the data's available. So that's why I started with the units, but then when you focus on your study area, make sure the unit is taken first. Sometimes you have your area and you have different points of observation data, not in your center. For example, this part is your area of interest, but the data is only available here and down. So what normally people do is interpolate the data. For example, IMD, rainfall data. So it is good to understand the data, the units, and then come back to your area of interest. And this area should be very, very carefully determined. Units have to be consistent. Again, the units, the area has to come concentrate with your area in your water balance, so which you should go back here and check. If you're using metric for length, like meters, centimeters, use your areas for as per your metric also, which is square meters, square kilometers, et cetera. Don't jump back and forth, square yards, square feet. You do use acres, right? In irrigation, you see suddenly acres coming up and the hectares on one side. So don't jump back and forth. I normally use meters, millimeters, centimeters, kilometers for length, and then jump into kilometer square, meter square, millimeter square, cubic meters, by area and volume respectively. So the volumes I use cubic meters, area I use meter square and length meters. Velocity, acceleration, all the meters. To keep it uniformly consistent, then you can easily divide or multiply by 10 or 900 orders to get into the other units. The area of unit has to be determined and units have to be consistent. Large scale with small scale, please understand that if you go larger scale, the probability of getting the data for your experiment is high. You'll have more options to get the data. However, if you have a smaller area, it might limit your probability. So make sure if you are okay for the small area and less data by interpolating or assuming from other data. For example, there's no rainfall here and there's no rainfall here. You're not gonna have rainfall here, right? Like some kind of assumptions that you can make. Depending on the distance, you don't have kilometers, but I'm saying 100 meters this side of your area, 100 meters this side of your area, you have observation for rainfall. You can carefully assume that this can also be zero. So those kind of assumptions. Basins, watershed, plot scales, et cetera. We did discuss about basins. What is a basin? What is a watershed catchment? Are you going to those scales or are you doing a plot scale analysis? Be very careful and do make these maps. GIS is a very good open source tool to make these maps for your study areas and then collect the data. But I would very carefully taking these examples from notebooks on if the data is available. If so, where is the data? And then my watershed area can be mapped out. Measurements and units, let's continue. Can also be larger scales when estimates are available. It can also show a bigger and clearer picture. However, if you do not have the data, then most probably people go above scale. For example, this is an annual precipitation map for 2008 that we prepared. And within your district, some places did not have rain gauge. For example, I may not have a gauge here. I may not have a rain gauge here, but it can be extrapolated into the district boundary, which AMD also does, to get an assumption of the rainfall. And you could see clearly a pattern. This region is getting rainfall around 674 to 851, whereas this is the driest with 340 to 353, and then yellows and blues, et cetera. So your estimates, if they are available, if the data is available, you can go to larger scale. If it is very focused and you're doing a field study, it is better to locate a smaller watershed area for your study and data units. Similarly, such maps can be made for other parameters to visualize. See, this visualization is a very important technique to understand your water balance. So if I see a map, which is a spatial representation of the data, rather than an equation, I could quickly say that, okay, this is the driest region. And around the driest region is also having less rainfall. So somewhere here that less rainfall, but higher rainfall is on the south of Gujarat. So I can throw these estimates or comments saying that South Gujarat has better rainfall because I visualized your data. Then I can do multiple data sets together to estimate the water balance and storage components. You can also do global water resource maps. For example, this map has been done by NASA to show how the groundwater availability changes across the world. And you could see based on the drainage areas, the basins, they've done these maps. And you could see centimeters equivalent of H2O. And you can see how it changes per month annual availabilities of groundwater resources. And you can see that, okay, red is mostly here and that is where it is more dangerous, the water resources, et cetera. So you could cloud these with your other estimates, be it observation data, be it your water availability data, to get at an estimate, a clear estimate of where you want to take your water balance. How do you estimate unknown parameters? And also if it is at one length, you cannot estimate the unknown parameters, are you okay to dismiss them as negligible? One such parameter is groundwater in versus groundwater out. Many equations you would see that groundwater in is assumed to be the groundwater out, so both of them can cancel. If it is a groundwater study, don't do that. Okay, because groundwater study is to estimate how much groundwater you're pumping and then looking at it in detail. So be careful with what your estimates are and what is your objective of your study. So measurements and units, also the unit for the area is always kept as a watershed. So most studies would keep the watershed boundary because it is easier for estimating the input. Let's say example rainfall, okay? In this equation, you'll see rainfall can be estimated very accurately and how the rainfall combines into discharge very accurately through a watershed approach. If you do not have a watershed approach, it might be difficult because the conversion of rainfall to a runoff is based on elevations, which also gives you the boundary of your watershed base in catchment. So understanding the hydrology flows through the physics equations and also the principle of water flows from high potential to low potential. And here a watershed boundary captures that dynamics from a high potential to low potential. So all this could be managed within your watershed if you know these physics principles and these are driving your watershed boundaries and area, et cetera, et cetera. So with this, I would like to conclude today's lecture and stress on the fact that units are very important for water balance. There are concerns that sometimes you may not have all the data for your water balance equations. For example, BEQ, et cetera, et cetera. So you are allowed to assume some values for your input or output variables, but clearly mentioned that. So that another study person or a researcher can understand how you've got these values and is it credible depending on your limitations. Also it is important to finalize a unit area for the study and normally it is a watershed approach. Or if you have more data you can go for state, district, national, subcontinent, global, et cetera. And when you grow above a particular level, like for example, from watershed to nation, some of these parameters can cancel out. And most of the time you won't have all the data. So be careful on picking the unit for your study area and then based on the units, also make sure you have all the data that is available for your study area and what are the parameter units available and from the parameter units, try to estimate what is a time unit and keep the time common across, keep the parameter unit common across so that you have something to compare and estimate your change in storage. So we've taken all these points and I would like to conclude with this lecture for important points on setting up a watershed, water balance balance. Thank you.